ABH antigen is the antigen that determines ABO blood type. ABO blood type is determined by the difference of ABO gene activity in glycosylated terminal having a specific structure. ABH antigen is mainly expressed on the surface of erythrocyte, so it is a major reason that causes rejection when different type of blood is transfused. It is also known that ABH antigen is expressed in diverse tissues including blood vessel, salivary gland, sweat gland, small intestine, large intestine, and pancreas, in addition to erythrocyte. In normal skin tissues, this antigen is found mostly in granular layer where differentiation of keratinocytes is most progressed and in the cells right before granular layer, while ABH antigen is hardly observed in spinous layer and basal layer (Ravn et al., APMIS 108:1-28 (2000); Lloyd, Glycoconjugate J 17:531-541 (2000); Greenwell, Glycoconjugate J 14:159-173 (1997); Dabelsteen et al., J Invest dermatol 82:13-17 (1984)).
ABH antigen is determined according to the structure of glycosylated terminal of protein or lipid. When N-acetylgalactosamine is conjugated on fucose-galactose terminal, the antigen is determined as antigen A (type A). When galactose is conjugated, the antigen is determined as antigen B (type B). When N-acetylgalactosamine and galactose are all conjugated, the antigen is determined as type AB. When N-acetylgalactosamine and galactose are not conjugated, the antigen is determined as antigen O (type O) (see FIG. 1). Therefore, histological expression is regulated by the expression of fucosyl transferase 1 or 2 (FUT1 or FUT2) that regulates the synthesis of the common fucose-galactose terminal.
Efforts have been made to explain the rejection response according to the blood transfusion with different blood type, and to disclose corelationship between the expression of ABH antigen and incidence of diverse diseases. However, none of these efforts have been successful so far, and the function of ABH antigen itself still needs to be studied.